Existing glasses-free flat panel 3D displays are based on technologies developed in the early 1900s (e.g., lenticular lens and parallax barrier). These displays have poor image quality and limited 3D capabilities. The current glasses-free flat panel 3D displays present a limited number different views (e.g., 5-9) of an image over a limited horizontal field-of-view (e.g., 20 degrees). When viewed within the ideal viewing range one sees two adjacent views simultaneously (one in each eye) which creates the 3D effect. Outside of this field of view the sets of views repeat (e.g., 1-2-3-4-5-1-2-3-4-5-1-2-3-4-5-1-2-3-4-5) which causes an uncomfortable transition zone when users see view 1 with one eye and view 5 with the other eye. This limited number of views prevents users from getting a full 160-180 degree 3D view of a scene and the transition zones and other visual artifacts (cross talk and moiré) make these displays unacceptable in most applications.
Generally, holography, and in particular electro-holography (moving images) have the potential to present a true 3D image from a flat screen display. Multiple user holographic displays do not exist today due to high pixel count, high bandwidth and high compute power requirements.
Existing holoform rear and front projection displays use a static holographic projection screen and a large number of individual projectors to create a 3D viewing experience. This is achieved by creating a hologram in only the horizontal direction while filling in the vertical plane by diffusion similar in performance to a standard projection screen. This one-dimensional hologram significantly reduces bandwidth requirements and can be achieved with computer power available today.
Existing holoform systems most often use a large number of individual projectors that make them large, noisy, power hungry and very expensive. As a result, the existing holoform systems are not commercially viable. Time multiplexing of a set of projectors in the existing holoform system typically requires a motor-driven image scanning system which results in additional artifacts (e.g., low luminance and blur). These time multiplexed holoform systems require laser illumination which introduces speckle in the image, and may provide safety concerns. The image quality in the existing time multiplexed holoform systems is low. Additionally, many exhibit reliability problems in addition to poor image quality.
Holoform generally refers to a horizontal parallax only 3D technology to direct different image information to each eye. In a holoform 3D system, a special directional scattering screen is used to limit where a viewer can see the appropriate image information. In a holoform 3D system, the holographic screen is typically horizontally segmented (vertically striped) with limited horizontal diffusion in each segment and high diffusion in the vertical direction. Thus light passing through each screen segment can be considered to pass unaffected along a horizontal axis while it behaves as a normal projection screen in the vertical direction. A projector illuminating this screen can effectively be considered a point source that contains image information. If only one projector were employed to illuminate such a screen any viewer would see only a single vertical stripe of the projected image (which is potentially different for each eye) where the vertical information (color and intensity) of the image at that horizontal position on the screen can be seen unaffected. A second projector will create a second stripe and when a sufficient number of projectors are employed in a horizontal arrangement a whole image will be seen over the entire screen that varies in each eye as well as every different viewing position in front of the screen. A small horizontal diffusion is added to each screen segment to improve horizontal uniformity and limit the number of projectors required to illuminate a full image on the entire screen.
Typically, when the image is different in each eye, 3D is perceived. This image information can come from the same projector or a different projector depending on the arrangement. Vertical stripes of image information are presented by each imager to fill the light field, for example, a viewing space. The field of view, for example, a horizontal angular limit where an image is visible, is typically controlled by the number of projectors, the magnification of each projection lens, and in some cases, the angular distribution of the image information. With a large angular distribution, image information can be presented over nearly 180° field of view. Such a large field of view will be required to work in any tiling application such as a video wall application.
In an existing holoform system a reasonably large number of independent projectors are typically used to illuminate the holoform screen. The existing systems remain costly because of the relatively large number of projectors that is required to illuminate a screen even with only a limited field of view.
One way to reduce cost is to time multiplex a smaller number of projectors to create the large number of images that would have been created by the individual projection systems. Existing time multiplexed holoform systems have moving optical elements, such as a scanning or rotating mirror or prism which can deflect each image to a different viewing zone. For these systems, a significant amount of time is required to actually move the mirror and to stabilize the mirror before a new image is projected onto it. This further limits the time light is projected and therefore the brightness of the image. Rotating the mirror or prism in a continuous fashion to eliminate the delay in projecting the new image causes the image to move across the screen as it is projected. This effectively blurs the image resulting in reduced contrast and resolution, and creates substantial 3D crosstalk because at least a portion of each image stripe crosses a stripe boundary as formed on the screen.